A grounds-crew member at Scottsdale Stadium wheels out safety screens for the start of the Giants' spring training workouts.

Photo: Darron Cummings, Associated Press

A grounds-crew member at Scottsdale Stadium wheels out safety...

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Chris Hughes waits for autographs from San Francisco Giants players after they arrived for spring training baseball, Tuesday, Feb. 12, 2013, in Scottsdale, Ariz. The pitchers and catchers for the defending World Champions start workouts on Wednesday. (AP Photo/Darron Cummings)

Photo: Darron Cummings, Associated Press

Chris Hughes waits for autographs from San Francisco Giants players...

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Giants' manager Bruce Bochy gets a spray of champagne while the team celebrates in the clubhouse, as the San Francisco Giants beat the Cincinnati Reds 6-4 in game five to win the National League Division Series in Cincinnati, Ohio on Thursday Oct. 11, 2012.

Photo: Michael Macor, The Chronicle

Giants' manager Bruce Bochy gets a spray of champagne while the...

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Brandon Belt will continue to get work in left field to keep his bat in the lineup on days when Buster Posey is playing first base.

Scottsdale, Ariz. -- Spring training officially can begin now that manager Bruce Bochy has thrown out the ceremonial first barb at reliever Jeremy Affeldt. As Bochy was discussing the World Baseball Classic, he said, "We encouraged Affeldt to go. We need a two-week break from him."

When Affeldt and 16 teammates throw their first bullpen sessions of spring training Wednesday, the Giants formally begin work toward what they hope is a second consecutive World Series championship and third in four years, a feat that few outside of Scottsdale Stadium see happening.

Las Vegas oddsmakers favor the Tigers, Dodgers, Angels, Nationals, Blue Jays, Yankees and Reds more than the Giants for winning the 2013 World Series.

Some of that skepticism stems from the sheer difficulty of repeating, some from the belief that the Giants should have done more to fortify the roster while the division-rival Dodgers continued their Park Avenue shopping spree for talent.

Beyond that is a commonly held notion that the Giants won another World Series not because they were the best team in the majors, but merely the hottest at the end.

"Once again, we're being doubted," reliever Sergio Romo said. "Once again, we're not getting any credit. Yeah, we had a couple of balls bounce our way, but we were prepared for those situations."

To the extent a team with two titles in three years can be considered underdogs, the Giants are. Few believe the Giants will win even the West.

Brandon Belt had an answer for that at FanFest when a fan asked a panel of players what they thought of the Dodgers' big acquisitions.

"You can't buy team chemistry," Belt said, a quote that quickly fell into the hands of L.A. fans with Twitter accounts. Some of their responses were unprintable, and Belt learned the hard way that people on social media are not always nice.

"Man," Belt tweeted Monday, "these guys are angry."

Belt laughed about the episode Tuesday as teammates filtered into the clubhouse on the official reporting date for pitchers and catchers. He wondered if starting a Twitter account was a good idea.

Belt will dress near Hunter Pence, who is eager to start his first spring training with the Giants.

"I heard a lot of people say this was a short offseason," Pence said. "I don't think it was short. I'm energized."

Know who really needs to be energized this spring? Center fielder Gary Brown, the Giants' first-round draft pick in 2010, who will get a lot of game action, especially when Angel Pagan and Andres Torres leave for the WBC.

Bochy said he wants to see a lot of Brown in left and right field, noting that the 24-year-old is "moving up the ladder" in the system and the Giants recently signed a center fielder (Pagan) for four years.

"I want to move him around a little bit and take a look at it," said Bochy, who reiterated that Belt will get a lot of work this spring in left field. Bochy expects Buster Posey to start about as many games at first base as last year (29) and does not want to lose Belt's bat on some of those days.

Beyond that, this camp will feature a few unsexy but important competitions.

Yusmeiro Petit and Jean Machi, both on the 40-man roster, lead a gaggle of relievers fighting for a final bullpen spot or two. Heath Hembree could be a dark horse if he can show he is caught up from last summer's elbow injury.